SAN DIEGO — Luis Castillo’s aching left foot has officially become a worry.

But the team can now add Castillo’s right foot to the equation, as manager Jerry Manuel revealed yesterday that his second baseman may have sustained an injury from favoring too much the bone-bruise he’s had on the left foot since spring training.

Manuel said a disabled-list stint for Castillo could be a possibility if the Mets don’t begin to see physical improvement from him.

“It’s something we talk about and something we’ll continue to talk about,” Manuel said before the Mets’ 18-6 loss to the Padres last night. “But we feel he can still play right now.”

Castillo, a day after delivering the go-ahead hit for the Mets in a 10-4 victory at Milwaukee, was absent from the starting lineup at Petco Park, giving Alex Cora the start at second base. As a pinch hitter last night, Castillo struck out in the ninth.

Manuel’s plan is to sit Castillo against right-handed pitchers, allowing the lefty-swinging Cora to take those at-bats and get Castillo rest.

*

Jon Niese appears ready for a return to the Mets’ rotation after pitching six innings yesterday in a rehab start for Triple-A Buffalo. The lefty is tentatively scheduled to start Saturday vs. the Marlins at Citi Field. He suffered a strained right hamstring on May 19.

*

John Maine, who played catch during the Mets’ last homestand, is expected to resume throwing activities today. Maine (shoulder tendinitis) has been on the DL since May 21.

The Mets are back to eighth inning by committee in the aftermath of Ryota Igarashi allowing a game-winning homer to Corey Hart on Friday in Milwaukee. Elmer Dessens pitched a scoreless eighth on Sunday, but he isn’t necessarily Manuel’s primary right-handed option in the eighth.